1. Field of the Invention
This invention relates to an image formation apparatus and an image formation method for decreasing density unevenness appearing on an image in later print if a developer support of an image formation apparatus is left to stand for a predetermined time or more without being rotated.
2. Related Arts
JP-A-2001-56601 describes the following art: In an image formation apparatus in which a development cartridge is placed, if a developer (hereinafter, called toner) stored in the development cartridge becomes unbalanced, to always restore the toner to a proper condition, if the development cartridge is a new product, a new development device startup mode is executed for idling as long as the time required for uniforming the toner and charging the toner; if the development cartridge is not a new product, a toner uniforming mode is executed for idling as long as the time required for uniforming the toner.
If a development roller of an image formation apparatus is left to stand for a predetermined time or more without being rotated and then print is started, density unevenness in the development roller period appears on an image, which will be hereinafter referred to as standing banding. The standing banding is determined by the relative positional relationship of the development roller to a development device with the development roller left to stand. For example, in a development device of a structure wherein a regulating blade is provided below a development roller provided in a development device housing opening opposed to a photosensitive body and a seal is provided above the development roller, when the development roller is left to stand without being rotated, the image density in the portion corresponding to the developing chamber side (in the housing), which will be hereinafter referred to as developing chamber portion, between the lower regulating blade and the upper seal in the development roller circumferential direction becomes high as compared with the portion exposed to the housing outside in the standing state, which will be hereinafter exposure portion, and appears as density unevenness like a band in the development roller period. This standing banding is not an everlasting phenomenon and appears the strongest on the first print sheet just after the standing. The density unevenness becomes inconspicuous every print sheet and as several sheets are printed, the standing banding disappears.
The degree of the standing banding changes depending on the duration of the standing time, the toner degradation degree, and the environmental condition. The longer the standing time, the more conspicuous the banding; the banding becomes noticeable particularly in high-temperature and high-humidity environments.
However, JP-A-2001-56601 proposes that idling is performed as long as the time required for uniforming the toner and charging the toner, but does not give any consideration to the standing banding.